Green lumber is typically dried under controlled conditions in a lumber kiln. While batch-type kilns are still widely used, a number of sawmills have upgraded to continuous flow kilns. A conventional continuous flow kiln is an elongate chamber with charge portals at opposite ends and rails that extend through the kiln and the charge portals. Green lumber is stacked onto carts outside of the kiln, and the loaded carts (“charges”) are moved end-to-end through the kiln along the rails.
Motive force to move the charges through the kiln is provided by a hydraulic or electric pusher. The pusher pushes a charge toward the entrance of the kiln and into contact with the lagging end of the series of charges. This advances the downstream charges a corresponding distance along the track toward the exit. As each successive charge is pushed into the entrance of the kiln, a downstream-most charge is advanced from the kiln through the exit at the opposite end. Some continuous kilns have only one track and one pusher, while others have a pair of parallel tracks and a corresponding pusher along each track.
Continuous flow kilns are relatively efficient in terms of energy costs and drying speed, and they can hold relatively large volumes of lumber. But like other lumber kilns, continuous flow kilns (and the lumber within) are vulnerable to interior fires and can thus be more difficult and/or expensive to insure.